Objectives We aimed to describe cardiac output (CO) trend from prepregnancy to post partum using an inert gas rebreathing (IGR) device and compare these measurements with those obtained by a pulse waveform analysis (PWA) technique, both cross-sectionally and longitudinally.
Methods Non-smoking healthy women, aged 18–44 years, with body mass index <35 were included in this prospective observational study. CO measurements were collected at different time points (prepregnancy, at four different gestational epochs and post partum) using IGR and PWA. A linear mixed model analysis tested whether the longitudinal change in CO differed between the techniques. Bland-Altman analysis and intraclass correlation coefficient (ICC) were used for cross-sectional and a four-quadrant plot for longitudinal comparisons.
Results Of the 413 participants, 69 had a complete longitudinal assessment throughout pregnancy. In this latter cohort, the maximum CO rise was seen at 15.2 weeks with IGR (+17.5% from prepregnancy) and at 10.4 weeks with PWA (+7.7% from prepregnancy). Trends differed significantly (p=0.0093). Cross-sectional analysis was performed in the whole population of 413 women: the mean CO was 6.14 L/min and 6.38 L/min for PWA and IGR, respectively, the percentage of error was 46% and the ICC was 0.348, with similar results at all separate time points. Longitudinal concordance was 64%.
Conclusions Despite differences between devices, the maximum CO rise in healthy pregnancies is more modest and earlier than previously reported. The two methods of CO measurement do not agree closely and cannot be used interchangeably. Technique-specific reference ranges are needed before they can be applied in research and clinical settings.
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Contributors CCL and JC have contributed to conception and design of the study. GM, LFF and JT have acquired the data. JC and DR have analysed the data. GM has drafted the manuscript. CCL, IBW and CMM have critically revised the manuscript. CCL is responsible for the overall content as guarantor.
Funding This work was supported by Action Medical Research, Samsung Healthcare, Imperial College Healthcare Trust Charities, Imperial College BRC and Genesis Research Trust. The funding sources had no involvement in the study design, collection of data and writing the article.
Competing interests CCL reports grants from Action Medical Research, grants and non-financial support from Samsung Healthcare, grants from Imperial College Healthcare Trust Charities and grants from Imperial College BRC, outside the submitted work.
Patient consent Obtained.
Ethics approval The two prospective observational studies were approved by the National Research Ethics Committee (’CONCEIVE': East of Scotland Research Ethics Service, REC reference 14/ES/1046; ’PRECEPT': National Research Ethics Service Committee London Riverside, REC reference 15/LO/0341).
Provenance and peer review Not commissioned; externally peer reviewed.